Nanotechnology may provide nanoparticles having various sizes, compositions, and shapes. For materials having catalytic activity, such as metal oxide, metal/metal oxide composites, and the like, nanoparticles may have useful characteristics compared to particles having a larger size.
Meanwhile, according to J. A. Rodriguez et. al., Science, Vol 318, pp. 1757-1760, 2007, which is incorporated herein by reference, pure Au(111) does not show catalytic activity to water-gas shift reaction (WGS) (CO+H2O→CO2+H2); however, in the case of coating the surface of gold in the degree of 20 to 30% with metal oxide nanoparticles such as ceria or titania, the activity thereof corresponds to that of good WGS catalyst such as copper(111) or copper(100). Further, according to Maria Flytzani-Stephanopoulos et al., Science, Vol 301, pp. 935-938, 2003, incorporated herein by reference, as a WGS catalyst, the activity for ceria-based Au and Pt is mentioned. In another example, according to Graham J. Hutchings et al., Science, Vol 311, pp. 362-365, 2006, incorporated herein by reference, during the solvent-free oxidation of a primary alcohol to aldehyde, Au—Pd(alloy)/TiO2 catalyst may be used. Au—Pd(alloy)/TiO2 may maintain high selectivity for benzaldehyde at a high conversion rate, which may not be observed in pure Au catalyst or pure Pt catalyst.
However, in using the catalysts, there may be problems to be solved, such as agglomeration of the particles.